In recent years, there have been growing demands for speedy and homogeneous production of functional thin films in various industries. One of the important challenges has been to establish a method for efficiently creating high-performance polycrystalline silicon films at low cost. Such films are expected to be practically used in the fields of “giant electronics”, such as thin film solar cells or liquid crystal thin film transistors (TFTs).
Compared with amorphous silicon used in conventional thin film solar cells or liquid crystal TFTs, polycrystalline silicon has many advantageous properties. For example, it is higher in carrier mobility, longer in carrier lifetime and free from light degradation. However, if a polycrystalline silicon film is to be used in a solar cell, it is necessary to make the film ten times as thick as the conventional ones, or even thicker, since its absorption coefficient for sunlight is smaller than that of amorphous silicon.
Conventionally, such polycrystalline silicon films are formed by chemical vapor deposition (CVD), in which a silicon-based material gas (e.g. SiH4 or SiF4) is decomposed by heat, plasma or the like to form the film (refer to Patent Documents 1 and 2 and Non-Patent Document 1).
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2002-270519
[Patent Document 2] Japanese Unexamined Patent Application Publication No. H08-008180
[Non-Patent Document 1] Tatsuo ASAMAKI, “Hakumaku Sakusei No Kiso” (Essentials of Thin Film Production), THE NIKKAN KOGYO SHINBUN, LTD., July 2005, pp. 234-273